Today there are several known ways of executing engine braking using a combustion engine, which methods are especially used for engine braking in combustion engines of heavy vehicles, such as diesel engines of buses and trucks. Engine braking is used in these types of vehicles for instance in long downhill slopes in order to avoid the risk of overheating the mechanical wheel braking devices of the vehicle which may lead to wholly or partial loss of braking effect.
One example of engine braking is realized by closing the exhaust air channel/exhaust gas channel by means of a valve, whereby the combustion engine continues to operate in four-stroke cycle, and when the outlet valves of the cylinder are opened, in order to evacuate exhaust gases during normal operation, a back pressure is generated downstream the cylinder. The back pressure is used to counteract the displacement of the piston from the lower dead centre to the upper dead centre when the outlet valves are open. However, this engine braking effect only corresponds to a part of the drive effect of the combustion engine, at the same time as this type of engine braking above all result in unwanted heating of the components of the combustion engine.
Engine braking according to conventional type entail that the combustion engine must have engine valve springs having high permanent spring force, which is not a problem in connection with conventional camshaft actuated engine valves since the high spring force is recovered on the back side of the cam, however it is devastating for an engine valve control without force recovery.
U.S. Pat. No. 7,946,269 to Gerum, disclose a combustion engine comprising a cylinder having a cylinder volume and a piston displaceable in said cylinder volume, and a storage volume that is arranged in controllable fluid communication with the cylinder volume via the inlet valves of the cylinders. The combustion engine is driven in four-stroke cycle during the engine braking and when the piston is displaced from the upper dead centre to the lower dead centre and the inlet valves are open, the fluid communication between the storage volume and the cylinder volume is opened. I.e. air having high pressure is provided during the intake stroke, whereupon engine braking takes place during the compression stroke. Thus, no engine braking takes place during the intake stroke, instead air having high pressure is provided that de facto counteract engine braking.